1. Field of the Invention
For variable currents charging, an apparatus detects the saturation status of a charging battery by monitoring the properties of energy consumption of the charging battery's equivalent resistance.
2. Description of the Related Art
Portable products such as cellular phones, notebook computers and related products, are increasingly popular. These portable products have increasingly improved functions thereby satisfying a wide range of consumers. As advanced as these products are, advances in improving battery operation time tends to fall behind the pace of innovation of the portable products themselves. At present there is much research focusing on extending the operation time of a battery by, e.g., saving power consumed by the products. Extending the operation time of a battery also increases the charging time of the battery. Therefore, it is desirable, to the extent possible, to decrease the charging time of a battery.
FIG. 1 illustrates a property curve diagram of the temperature variation and the charging battery voltage variation with charging time variation. The figure focuses on a fixed amount of charging current (2500 mA) and ambient temperature of 10.degree. C., 25.degree. C., and 45.degree. C.
Referring to FIG. 1, the solid line A represents the charging battery voltage variation with the charging time for the ambient temperature 10.degree. C. and a fixed charging current of 2500 mA. The solid line A rises smoothly from the initial voltage 10.5 V to the saturated voltage 12.8 V, and the corresponding time is between 80 and 90 minutes known as saturated time. The solid line B represents the battery temperature variation with the charging time for the ambient temperature of 10.degree. C. and the fixed charging current of 2500 mA; initially, the charging battery temperature curve, solid line B, rises smoothly, and then tends to be even between 30 and 80 minutes of the charging time but when it arrives at the saturated time, the charging battery temperature rises suddenly. The dotted line C represents the charging battery voltage variation with the charging time for the ambient temperature 25.degree. C. and the fixed charging current of 2500 mA. The dotted line C rises smoothly from initial voltage 10.5 V to the saturated voltage 12.5 V. The dotted line D represents the battery temperature variation with the charging time for the ambient temperature of 25.degree. C. and the fixed charging current of 2500 mA. Initially, the dotted line D rises smoothly and then tends to be even between 30 and 80 minutes of the charging time; when it arrives at the saturated time, the charging battery temperature rises rapidly. Other dotted lines E and F, respectively, represent battery charging voltage and temperature variation with charging time for the ambient temperature of 45.degree. C. and the fixed charging current of 2500 mA as described above.
In view of the above, when charging up a battery, the battery temperature increases as the ambient temperature increases. The battery charging voltage decreases as the ambient temperature increases. When a charging voltage curve line arrives at saturation, the battery temperature rises rapidly. Because the charging battery's saturating voltage will be changed by ambient temperature variation, it cannot be a dependable factor for judging battery saturation.
According to the properties of a charging battery, present apparatuses for detecting charging status usually only check the charging battery temperature with respect to whether it has risen rapidly. In other words, conventional devices check the saturated status by means of the slope of charging battery's temperature.
FIG. 2 only changes the charging current of FIG. 1 from 2500 mA to 1000 mA. The solid line A' represents charging battery voltage variation with the charging time for ambient temperature of 10.degree. C. and a fixed charging current 1000 mA. By changing the charging current to 1000 mA, the saturating time is extended from 80 to 200 minutes, and the saturating voltage decreases from 12.8 V to 12.3 V. The solid line B' corresponds to A' of FIG. 2. As shown, when the charging time arrives at 200 minutes, the slope of the battery temperature increases suddenly. The dotted lines C', D', E', and F' respectively correspond to the dotted lines C, D, E and F of FIG. 1, except that the charging current is changed from 2500 mA to 1000 mA.
As shown in FIG. 1 and FIG. 2, both the ambient temperature variation and charging current variation have an impact on the saturated voltage and the charging time. Specifically, when the charging current increases more, the charging time decreases more. But when the charging current is lower, the charging time is more extended, and the battery temperature curve line is more flat. In other words, if charging current is much lower, the battery temperature curve line is too flat to judge saturated status by the slope of the battery temperature curve line. In contrast to relatively lower charging current, if the charging current is relatively high, then the battery will be overloaded and burned.
FIG. 3 shows a prior art block diagram of a nickel-hydrogen or a nickel-cadmium battery. An adapter 31 transforms the power from an alternating current (AC) voltage to a direct current (DC) voltage, and supplies both a consuming apparatus 32 and a charging apparatus 37 herein comprising a DC controller 33 to transform the DC voltage of the adapter 31 into the DC current herein and charging up the battery by passing to a current sensor 34. At the same time, a detecting apparatus 36 monitors the temperature variance of charging battery 35 at particular time to control the DC controller 33 to continue the charging operation.
FIG. 4, which is related to FIG. 3, shows a flow chart diagram illustrating a charging method in which step 41 resets time t, step 42 accumulates time t until step 43 at which t equals a fixed reference time T, and then step 44 judges the rising slope of battery temperature (dT), namely, whether it is greater than a fixed reference value N and, if so, thereby ending the charging operation or whether the process should return to step 41.
Thus, in the prior art, the charging battery is deemed saturated by focusing on battery temperature variance in a fixed time for a fixed current charging operation.
Referring to FIG. 1 and FIG. 2, when a charging current increases, charging time decreases. However, the amount of charging current is still restricted within a maximum charging. Even though many portable products such as notebook computers need to hold enough power to operate all functions including CPU (central process unit) requests, the charging apparatus typically adopts a minimum charging current to process charging up the battery. For example, a maximum charging current is usually 2500 mA for a nickel-hydrogen or nickel-cadmium battery for a notebook computer, but its charging current is often kept at 1000 mA. Therefore, even if several components of the consuming apparatus 32 are idle, the current not in use cannot be offered to the charging apparatus to accelerate charging time. If more current is offered to the present fixed current charging apparatus, then it is easy to misjudge the battery saturated status due to the sudden change of the amount of charging current which induces a sharp variable slope of the battery temperature.